Antenna system



Dec. 28, 1.948. F. o. cHEsus ErAL ANTENNA SYSTEM 2 Sheets-Sheet 1 Filed July 31, 1945 Mln/c0701? INVENTORS. FRANK 0. CHESUS F'RAIVK G. THOMAS Dec. 28, 1948. F, 0, CHESUS ETAL 2,457,l26

ANTENNA SYSTEM 2 Sheets-Sheet 2 Filed July 31, 1945 v INVENTORS. FRANK o. cHEsus FRANK G. THON/1.5

`BY ATORNLY Patented Dec. 218, 1948 ANTENNA SYSTEM Frank 0. Chesus, Jackson Heights, and Frank G.

Thomas, Islip, N. Y., assignors to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application July 3l, 1945, Serial No. 608.048

9 Claims. (Cl. 343-115) The present invention relates to antenna systems, and particularly to those adapted for use with direction nders.

In'antenna systems for portable direction ilnders, particularly those carried on airplanes, certain special conditions must be met: the desiderata for such collector systems include light weight and small volume (to lessen wind resistance). While some means for indicating sense is required, the use of sensing antennas and coupling arrangements therefor add materially to both the weight and volume of the antenna system.

An object of the present invention is the provision of a novel antenna system particularly one adapted for direction finding applications and characterized by relatively light weight and small volume.

Another object of the present invention is the provision of an Adcock type direction finding antenna system which dispenses with the use of an extra antenna for sense indication and therefore avoids any coupling arrangements for said extra antenna.

In accordance with our invention the Adcock array is used in a somewhat conventional manner for obtaining a line of direction. To obtain a sense indication, however, the voltages induced in the antenna units of the antenna system, which voltages are taken with respect to ground are algebraically added, and thereby an omnidirectional pattern is produced which is combined with the crossed figure-of-eight pattern of the usual Adcock array to produce sensing indications.

According to one aspect of .our invention, the Adcock array is balanced with respect to ground for direction finding purposes. However, when utilizing all of the antenna units of the Adcock array for sensing purposes, the voltage taken from these units is unbalanced with respect to ground. v

' still further object of the present invention is the provision, in an Adcock array, of a sensing arrangement making use of the direction finder *l antenna units in which the output of the sensing arrangement is balanced with respect to ground.

`ther and further 4objects of the present invention will become apparent and the invention will be best understood from the following description of an embodiment thereof, reference being had to the drawings, in which:

Fig. 1 is a schematic and block diagram of a direction finder embodying oux` invention; and

dit

50 zontal.

2 Fig. 2 is a theoretical drawing used in explaining the operation of the direction ilnder of Fig. 1.

Referring now to the embodiment of our invention illustrated in Fig. l, the antenna system includes four spaced vertical antenna units i-B,

in the form of dipoles, separated into two pairs 5 and of interconnected-units, pair 5 consisting of units i and 2 and pair consisting of units 3 and d. While thel pairs are illustrated as separated in Figs. 1 and 2 tor the purpose of more clearly showing the connections of the system, in actual practice, the pairs are crossed at right angles to each other so that' the dipoles are lsymmetrically disposed around a central axis and are equi-distant from said central axis and from each other, to produce a crossed gure-ofeight reception diagram.

For the antenna units, it is preferred, to use balanced antennas having a substantially omnidirectional radiation pattern, as for example, the

type of dipole described in the copending application, F. 0. Chesus, for Direction finder, Serial No. 613,329, filed August 29, 1945, now Patent No. 2,454,774, granted November 30, 1948. lliach4 of the antenna units l-t consists o three cylindrical conductors coaxially arranged: an inner conductor l, an intermediate conductor t, and an outer conductor d. The intermediate conductor d extends beyond conductors i and s and .may be twice as long as they are. The top of the inner conductor l is connected by a resistance l@ to the outer surface of the outer conductor s adjacent the top thereof. The value of resistance i0 is chosen in relation to the other parameters of the antenna system so that the usual requirements,

such as impedance matching, are satisfied. The radiating surfaces of this unit include the outer surface of outer conductor t and the exposed portion of intermediate conductor E. This lunit is .characterized by small volume, light weight and 'f operates satisfactorily over a relatively wide band of frequencies.

Antenna units i and 2 are cross-connected by a shielded dual transmission line li and antenna units t and Il are cross-connected by a shielded dual transmission lline i2, each of said lines ii and i2 being substantially in the form of a U, the sides of which are substantially vertical and the bottom portion of which is substantially hori- Line ii includes inner conductors I3 and It and outer shield It, while line l2 includes inner conductors I6 and il and outer shield i8.

Transmission lines Il and l2 are connected to l the lower ends of the antenna units i-t as follows:

nner conductor Il connects together the inner conductors 'I of antenna units .I and 2 while inner conductor I1 connects together the inner conductors 1 of antenna units 3 and 4. The ends of inner conductors I3 and IB are connected to the outside of the outer conductors 9 of antenna units I and 2, and 3 and l respectively, conductors I3 and I6 being open as indicated at I9 and 20 respectively, the loose ends being con: nected through shielded dual transmission lines 2| and 22 respectively to a goniometer 23 of any suitable type. To enable making these connections, metallic shields IB and I8 are broken away adjacent portions I9 and 20, which are the midpoints of the horizontal sections of the transmission lines I'I and I2 respectively and these portions are enclosed within a metallic junction box shown in broken lines and designated by the numeral 24, the shields of transmission lines II and I2, as well as 2| and 22, being grounded tosaid junction box.

The outputof goniometer 23, is fed to a direction finding receiver whose output is fed to an indicator 26 which may be a cathode ray oscillograph tube arrangement. This arrangement is adapted to give a line of direction indication, but there is an 180 ambiguity which requires some sensing arrangement for its correction.

In accordance with our invention, the same antenna units I-d are-also used for sensing purposes. Furthermore, in accordance with our invention, these antenna units are so interconnected that the output for sensing purposes is balanced with respect to ground. .In accomplishing this, the midpoint of inner conductor Iii of line I I is connected by conductor 21 to atrans` mission line transformer 28 while the midpoint of inner conductor I1 of line I2 is connected by conductor 29 to another transmission line transformer 30.

Transformers 28 and 30 may be in the form of short lengths of coaxial cable, substantially less than a quarter wavelength at the mean operating frequency, which are housed within junction box 24. Conductor 21 is connected to the inner conductor of coaxial cable 28 at one end thereof, the outer conductor of said cable 28 being connected at the same end to a conductor 3| forming part of a shielded dual transmission line 32 connected to the receiver 25. At the opposite end of cable 28, the inner conductor and the outer conductor thereof are connected together and to ground as indicated at 33. In order to provide for a balancedto-ground output, from the sensing arrangement to the direction finding receiver, transformer or cable serves as a phase inverter. For this purpose conductor 29 is connected to one end of the inner conductor of cable 30, the outer conductor at said end being connected to ground, and at the opposite end the inner conductor is connected to ground whereas the outer conductor is connected to an output conductor 3d forming part of the dual shielded transmission line 32. The impedance of transformers 28 and 30 should preferably be the same in order that the system may be balanced. Within the direction finding receiver 25, the output of conductors 3| and 34 may be combined through a relay 35 with the output of the goniometer 23 solas to produce a sensing indication in the indicator 2B. When sensing is not required, the relay is open in order that the line of direction may be more readily determined. The length of the shielded transmission line 32 is preferably such as to produce the required 90 phase shift bereceiver, the difference tweentheenergy derived from the goniometer and the energy from said line 32. In order to adjust the balance of the arrangement, a variable condenser 36 may be arranged across the conductors 33 and 3l.

Referring now to the theoretical diagram of Fig. 2, and assuming that a wave transverse to the plane of antenna units l and 2 and having a field indicated by the arrow 31 strikes both antenna units simultaneously, the tops'of each unit will tend to be positive at a given instant and the bottoms negative with respect thereto. At such instant therefore, with conductor I4 connecting the positive sides of the antenna units I and 2 together, the negative voltages thereof oppose each other through transmission line 2| in the goniometer. Consequently it will be seen that the goniometer receives the difference between the voltages induced in antenna units I and 2 in relation to their opposite poles. With the field described, the difference between these voltages will be zero while the difference between the voltages induced in antenna units 3 and l will have some ilnite value. On the other hand, assuming that a wave transverse to the plane of antenna units 3 and 4 and having a field indicated by the arrow 38 strikes antenna units 3 and s simultaneously, the difference between the voltages induced in antenna, units 3 and 4 is applied over lines 22 to the goniometer. With the Wave transverse to units 3 and d, this difference will equal nero. The difference between the voltages induced in antenna units I and 2 under these conditions, will have a finite value.

In the goniometer and the direction nding voltages derived from antennal units i-li are compared to obtain a directional indication in the indicator 26. For sensing purposes, however, the algebraic sum of the voltages in units I and 2 with respect to ground arer taken by line. 21 and applied to transformer 28. Likewise the algebraic sum of the voltages induced in antenna units 3 and 4 with respect to ground, are taken over conductor 29 and applied to transformer 30. In transformer 30 the voltages carried by conductor 29 from antenna units 3 and 4 are inverted with respect to ground whereas in transformer 28 they are not. Consequently lines 3| and 34 carry the sensing voltages derived from antenna units I-4 in a balanced-to-ground system. Since the directional indications are likewise maintained balanced-to-ground, the sensing and directional energy can be combined in the receiver.

While we have shown the specific details of a direction nder embodying our invention, it will be apparent to those versed in the art that numerous changes may be made in these details without departing from the teachings of our invention. For example, conventional type dipoles or other balanced antennas may be used instead of those hereindescribed. Other types of transformers other than those illustrated may be employed and as a matter of fact, the transformers may be dispensed with ,and any suitable known phase inverting means utilized to produce the balanced-to-ground sensing output. Accordingly, while we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of our invention as defined in the accompanying claims.

Weclaim:

1. A direction finder comprising two separate cross-connected pairs of spaced antenna units, means taking the difference between the voltages induced in the units of one pair, means taking the diierence between the voltages induced in the units of the other pair, means comparing said differences to produce -a directional indication, and a sensing arrangement including means taking the algebraic sum of the voltages induced in all of said units.

2. A direction nder comprising two crossconnected pairs of spaced antenna units, means taking the difference, balanced as to ground, between the voltages induced in the units of one pair, means taking the difference, balanced as to ground, -between the voltages induced in the units of the other pair, means comparing said diierences to produce a directional indication, and a sensing arrangement including means taking the algebraic sums of the vvoltages induced in said units with respect to ground and converting them into balanced-to-ground voltages.

3. A direction iinder comprising two crossconnected pairs of spaced antenna umts, means taking the differencebalanced as to ground, between the voltages induced in the units of one pair, means taking the ldierence, balanced as to ground, between the voltages induced in the units of the other pair, means comparing said differences to produce a directional indication,

and a sensing arrangement comprising means taking the algebraic sums of the voltages induced in said pairs with respect to ground, said lastmentioned means including means for inverting the phase of the voltages derived from one of said pairs with respect to ground to provide balanced-to-ground voltages from both pairs. and means for combining said balanced-to-ground voltages with the dinerence voltages in -the comparison means.

4. A direction nder comprising two separate cross-connected pairs of spaced vertical antenna unitsl symmetrically disposed around a central axis, means taking the difference between the voltages induced in the umts of one pair, means taking the diirerence between the voltages induced in the units of the other pair, means comparing said differences to produce a directional indication, and a sensing arrangement including means taking the algebraic sum of the voltages induced in all of said units.

5. A direction nder comprising two crossconnected pairs of spaced vertical antenna units symmetrically disposed around a central axis, means taking the diierence between the voltages induced in the units of one pair, means taking the dierence between the voltages induced in the antenna units of the other pair, means for comparing said differences to produce a directional indication, said difference voltages being balanced with respect to ground in the comparison means, and a sensing arrangement including means taking the algebraic sum of the voltages induced in all of said antenna units with respect to ground, means for balancing said` algebraic sum voltages with respect to ground, and means forcombining said algebraic sum voltages with the difference voltages in the comparison means.

6. A direction ilnder comprising a pair of spaced vertical dipoles, means taking the difference between the voltages. induced in one of the poles with respect to the other pole of one dipole metrically disposed around a central axis, means taking the difference between the voltages, in-

duced in one of the poles with respect to the other pole of one dipole of each pair, and the like voltage of the other dipole of said pair, means comparing saidv differences to produce a directional indication, and a sensing arrangement including means taking the algebraic sum of the voltages induced in all of said dipoles with respect to ground.

8. A direction finder comprising two crossconnecting pairs of spaced vertical dipoles symmetrically disposed around a central axis, means taking the difference between the voltage, induced in one of the poles with respect to the other pole of one dipole of each pair, and the like voltage ci' the other dipole of said pair, the output of said means being balanced with respect to ground, means comparing said differences to produce a directional indication, and a sensing arrangement including means taking the algebraic sum of the \o.tag'es induced in one pair of said dipoles with respect to ground and the algebraic sum of the voltage induced in the other pair of said dipoles lwith respect to ground, and means for inverting with respect to ground the phase of said algebrac sum of voltages from said one pair of dipoles to, thereby produce an output for sensing purposes from both pairs of dipoles which is balanced with respect to ground.

9. A direction nder comprisingtwo crossconnecting pairs of spaced vertical dipoles symmetrically disposed around a central axis, a

goniometer, means coupling the corresponding poles of the dipoles of each pair separately to the goniometer, a direction nding receiver coupled to the output of the goniometer, an indicator coupled to the output of the direction nding receiver, a transmission line transformer, a conductor cou- V pling the other poles of the dipoles of one pair together and to said transformer, a transmission line phase-inverting ductor coupling the other poles of the dipoles of the other pair together and to said transmission line phase-inverting transformer, both of said transformers being coupled to ground to produce a 'transformation of the voltages in the dipoles with respect to ground, the phase-inverting transformer inverting the phase of s'aid voltages with respect to ground and means for combining the outputs of said transformers with the output of said goniometer.

FRANK O. CHESUS. FRANK G. THOMAS.

REFERENCES CITED The following references are of record in the file of thispatent:

UNITED STATES PATENTS Sullinger et al Sept. 26, 1939 transformer, a second con- 

